Tropical hibiscus provides spectacular flowers

Richard Bogren, Gill, Daniel J.  |  5/30/2012 12:22:06 AM

For Release On Or After 06/15/12

By Dan Gill
LSU AgCenter Horticulturist

No other summer-flowering shrub surpasses the tropical hibiscus (Hibiscus rosa-sinensis) for glossy, dark green foliage and nonstop flowers in shades of and blends of pink, yellow, orange, white, lavender or scarlet. And their exceptionally long blooming season runs from late spring through late fall.

Tropical hibiscuses can be planted in the ground or in containers. When planting in the ground, the beds should be prepared by digging in generous amounts (2- to 3-inch layer) of compost, peat moss or manure and a light application of a general-purpose fertilizer.

Plant hibiscuses in the ground any time during the summer. Slightly untangle tightly packed root balls to encourage roots to spread into surrounding soil, and set the plants at the same level they were growing in the container. Because tropical hibiscus plants are not reliably hardy in Louisiana, those planted in the ground are subject to injury or loss when winter temperatures go below the mid-20s. Keep this in mind when deciding how many and where to use these plants in the landscape.

Hibiscuses make outstanding container plants, and you can bring them in on nights when freezing temperatures occur. When you bring your new plant home, check the root ball. If it is very potbound, shift it into a container about one-third larger than the one in which it is growing. Otherwise, wait until later to repot it because hibiscuses tend to flower better if not allowed too much root room.

During summer, fertilize your plants occasionally to keep them growing and blooming vigorously. Fertilize hibiscus plants growing in the ground using a granular, soluble or slow-release fertilizer according to label directions. Those in containers should be fertilized with your favorite soluble or slow-release fertilizer formulation. Do not use high-phosphorous fertilizers.

Hibiscuses prefer an even supply of water and should not be allowed to wilt. Those in containers are especially vulnerable to drying out and may need daily watering in summer. Water hibiscus plants growing in the ground regularly and thoroughly during hot, dry weather.

Providing enough light is especially important for abundant flower production. Hibiscus should be given as much direct sunlight as possible – at least six hours a day. Eight hours of sun is preferred.

Pruning may be done anytime you feel the need to control or shape the bushes. How far back you cut depends on what you trying to accomplish. Flower production will stop until the plant has made sufficient new growth. Generally, the farther back you cut your plant, the longer it will take to come back into flower. So it’s better to prune lightly occasionally than to allow the plant to grow considerably too large and have to prune more severely.

Yellow leaves often occur. And while alarming, they may not necessarily signal trouble. It is perfectly natural and healthy for a vigorously growing hibiscus to occasionally have its older leaves turn yellow and drop. Leaves may also yellow and drop due to sudden changes in environmental conditions and may occur in a newly purchased hibiscus or those moved from one location to another.

Yellowing leaves also may indicate a problem. A plant that is allowed to wilt may recover when watered but then drop leaves sometime later. An overall pale, yellowish look to the plant indicates a need to fertilize. Yellow leaves also may mean the plant is infested with sucking insects – generally aphids or whiteflies. Look carefully for these pests, and if you see any, use a pesticide labeled to control them. Several applications may be necessary.

Flower bud loss is most likely due to stress from such factors as high temperatures, dry soil, low light, sudden environmental changes and transplanting. Some hibiscus varieties seem to be more prone to bud drop than others.

Sometimes a healthy hibiscus will grow well but not produce flowers. As usual, several factors may be responsible. This may occur when newly purchased plants are repotted into a larger container or planted in the ground. This also may occur when plants are cut back severely. Under good growing conditions, the plants will eventually come into flower.

Insufficient light is another cause of poor flowering. Remember to give you plants as much direct sun as possible. Short days and cool temperatures also reduce flower production.

Dwarf hibiscuses pack all the punch of larger plants in a much smaller package. They are ideal for window boxes, containers and flower beds. Provide them the same care as for standard hibiscus, and enjoy the large colorful flowers produced on compact plants. There is, however, a catch. Dwarf hibiscus plants are not smaller-growing by nature B that is, they are not genetically dwarf. Instead, these are standard-size hibiscus plants that have been treated with plant growth regulators. Eventually, the treatment will wear off (it generally lasts about one growing season), and the plants will begin to grow at their normal rate. At that time, move them to a location where a larger plant would be appropriate.

Rick Bogren
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